Condensation reduction in fluid mixing

ABSTRACT

Methods and apparatus are disclosed for mixing fluid streams of different compositions to minimize fluid condensation inside a mixing vessel where the objective is to produce an all-vapor mixture product.

FIELD OF THE INVENTION

The present invention relates generally to improved methods for creatinga vapor stream by mixing fluid streams of different compositions so asto reduce or minimize fluid condensation and possible related corrosion,and to a fluid mixing vessel specially designed for practicing the fluidmixing technology of this invention. The improved methods generallycomprise the steps of introducing a hot vapor into an annular-shapedshell or baffle region surrounding a fluid mixing region at a pointproximate to an outlet end of the mixing region, and thereafter flowingthe hot vapor through the shell region to an inlet end of the mixingregion before mixing the hot vapor with one or more fluids, which aretypically cooler, flowing or being injected into the mixing region atthe inlet end thereof. The baffle essentially shields the entireinterior pressure wall of the mixing vessel from possible contacts withboth the injected stream(s) and the fluid mixture in the core of themixing vessel, while the hot vapor in the baffle region keeps the bafflehot enough to prevent condensation on the mixing region side of thebaffle.

The methods and apparatus of this invention have particular utility insituations where the mixing of fluid streams at different temperaturescan result in the condensation of a fluid that is highly corrosive tothe surrounding environment. A particular application of the presentinvention, although the present invention is not limited to suchapplication, is in mixing an alkali-containing fluid (liquid or vapor)with a steam feed stream to a catalyst-packed dehydrogenation reactor inconjunction with practicing the catalyst stabilization technology taughtby U.S. Pat. Nos. 5,461,179; 5,686,369; 5,695,724 and 5,739,071, whichpatents are incorporated herein by reference.

BACKGROUND OF THE INVENTION

In chemical process operations, there are various instances in which itis desired to mix fluids at different temperatures, typically a vapor atthe higher temperature with a liquid at the lower temperature, wherebythe liquid is vaporized by contact with the hot vapor. Particularlywhere the liquid, when in liquid form, is highly corrosive to thesurrounding environment, such as to vessel walls, valves, and the like,it is desirable to vaporize the liquid as quickly as possible and toreduce or minimize condensation that could cause corrosion of theequipment. One important application of these principles is inconnection with the in-situ stabilization and/or regeneration ofcatalyst used in dehydrogenation processes.

For example, as described in U.S. Pat. Nos. 5,461,179; 5,686,369;5,695,724 and 5,739,071, adding an alkali metal to the feed of acatalytic dehydrogenation reaction system can regenerate and/orstabilize the activity of the catalyst. A prime application of the basicprocess concept in the above patents is for the dehydrogenation ofethylbenzene to styrene in the presence of steam over a potassiumpromoted iron oxide catalyst. In this case, potassium is added to areactor feed stream to improve both the conversion of ethylbenzene andthe selectivity to styrene, as is described in the examples given inthese patents. This potassium can be introduced either as potassiummetal or a potassium compound such as potassium hydroxide (KOH). Ifmetal is used, it can be introduced into the reactor feed as a solid,liquid (melting point 64° C.), or a vapor (normal boiling point 774° C.)and, when the potassium metal contacts the steam in the reactor feed, itconverts to potassium hydroxide. If potassium hydroxide is used, it canbe introduced as a solid, liquid (melting point 406° C.), or as anaqueous solution. No matter what the source of potassium, however, thepotassium should be vaporized completely and mixed thoroughly with thereactor feed prior to the feed reaching the catalyst in the reactor forimproved or optimum results.

Potassium metal is highly reactive; and thus, for safety reasons,potassium hydroxide will in many cases be preferred over potassium metalas the source of potassium in a commercial catalyst stabilizationoperation Compared with using solid or melted potassium hydroxide,aqueous potassium hydroxide solutions will in many cases be preferredbecause of the ease of handling an aqueous liquid at ambienttemperatures.

One difficulty with using potassium hydroxide, however, is that it canbe very corrosive, especially at elevated temperatures, either as anaqueous solution or as melted potassium hydroxide. Once the potassiumhydroxide is fully vaporized and stays in the vapor phase, corrosion istypically much less of a problem If an aqueous solution is injecteddirectly into the main process piping, then corrosion of the mainprocess piping and equipment is possible. The KOH solution will contactthe vessel walls because the short distances between solution injectionpoint and the pipe walls typically will not allow adequate vaporizationtime before the potassium hydroxide, as solution, solid or liquid salt,reaches the walls. Furthermore, if the injection system is directly partof the main process piping, then the dehydrogenation process must beshut down if maintenance is required for the injection nozzle assembly.

To avoid damage and downtime for the dehydrogenation process unit, whichis often a large and expensive process unit, we have found in accordancewith this invention that it is advantageous to take at least a part ofthe steam being fed to the dehydrogenation process, vaporize thepotassium hydroxide into it, and then mix this potassium-rich steam withthe rest of the reactor feed. To vaporize the KOH solution, thepotassium hydroxide solution can be sprayed into the steam portioninside a small, dedicated “mixing vessel,” which can be shut down forperiodic maintenance without shutting down the entire dehydrogenationprocess. If the mixing vessel and spray nozzle assembly are designedproperly, the KOH solution droplets can be vaporized before the dropletsreach the walls of the vessel or the vessel outlet pipe, thereby, atleast in theory, reducing or minimizing corrosion caused by unvaporizedsolution However, in our experience of utilizing such systems, we havefound that this approach is insufficient by itself to avoid significantcorrosion of the mixing equipment.

Part of the problem of using potassium hydroxide in such applications isthat its vapor pressure is low even at the high dehydrogenation reactiontemperatures. At 598° C., which is the reactor inlet temperature ofExample 1 in previously mentioned U.S. Pat. No. 5,461,179, for example,the vapor pressure of potassium hydroxide is only 10 pascals. If thetotal pressure is 100 kilopascals at this temperature, then theconcentration of potassium hydroxide in the vapor phase cannot exceed100 parts per million on a molar basis even at this high temperature. At514° C., the saturation concentration would be only 10 parts per millionon a molar basis. Thus, the potassium must be diluted by relativelylarge amounts of high-temperature steam to get the potassium totallyinto the vapor phase.

Even if the average conditions of the steam fed to the mixing vessel areadequate to vaporize the aqueous potassium hydroxide solution, however,we have found that the potassium hydroxide vapor can re-condense if theinterior surface temperature of the mixing vessel walls is below the dewpoint of potassium hydroxide. Such condensation on the mixing vesselwalls can cause severe corrosion because of the highly corrosive natureof liquid potassium hydroxide at the high temperatures needed forvaporization.

Although it might be expected that the temperature of the walls in sucha mixing vessel would be nearly the same as that of the vapor passingthrough the interior, we have found that the wall temperature can besurprisingly colder than the average steam temperature. We attributethis to the following technical factors: 1) heat loss to the environmentthrough the walls, even with a thick layer of external insulation, canbe substantial; 2) heat loss is almost always even higher at vesselnozzles and supports and 3) heat transfer from the steam to the wallscan be poor because of the low steam velocity resulting from the vesselvolume and geometry needed for complete vaporization of the KOH solutionwithout impinging droplets on the walls. We have determined that thedifferential temperature between the vapor in the interior of the mixingvessel and the wall of the vessel can be in the range of 50 to 100° C.for conventionally-designed vessels insulated according to industrialstandards for energy conservation.

In practice, parts of the mixing vessel walls can be significantlycolder than this at vessel support points and at vessel nozzles whereheat loss can be greater and/or heat transfer from the process steam canbe slower. For example, the temperature of a manway lid in such a vesselcan be substantially colder than the walls of the main part of thevessel because there is no flow past the manway lid due to the fact thatit is in a cul-de-sac. In contrast, the wall temperatures of regularcylindrical pipes usually will be close to the temperature of thecontained fluid flow because the economic sizing of pipes typicallyresults in significant fluid velocities, which result in good heattransfer and thus low temperature differences between the contained flowand the pipe wall.

We explored a number of possible approaches to try to solve this problemof condensation due to “cold” vessel walls using commercially availableequipment and by adapting conventional technologies. As discussed below,none of these approaches proved to be entirely satisfactory.

First, we considered increasing the steam flow, which decreases thedew-point temperature of the potassium hydroxide vapor by diluting itand decreases the temperature drop somewhat of the steam through thesystem due to heat loss if the heat loss does not increaseproportionally more than the increase in the steam flow. However, wedetermined that increasing the steam flow results in a proportionallylarger mixing vessel so as to maintain the vessel residence time neededfor droplet vaporization; heating costs for the overall process increasebecause heat losses are increased with the larger mixing vessel andlarger diameters of the associated piping; and, even beyond the cost ofmaking up for additional heat loss, the cost of heating for the overallprocess is larger because the efficiency of heating this small steamflow for the mixing vessel typically will be lower than for thedehydrogenation process. Thus, increasing the steam flow enough to makea significant difference in corrosion protection substantially increasesboth the capital and operating costs.

A second approach we considered was that perhaps the mixing vessel couldbe insulated more effectively to lower the heat loss and, thus, increasethe vessel wall temperature. However, we determined that increasinginsulation thickness results in diminishing returns; and, at hightemperatures, heat loss still can be substantial even with thick layersof insulation. Also, heavily insulated nozzles and manways on vessels athigh temperatures can be problematic because if the nozzle flange boltsare under the insulation and kept very hot (above about 565° C. forstainless steels) they become loose because of high temperature “creep”whereby the bolt metal permanently stretches because of the combinationof tension imposed from tightening and temperature. Once they stretch,the bolts do not put sufficient force on the flanges to the vesselsealed. Therefore, there is an incentive to not heavily insulate theflanges, but this practice leads to high, localized heat losses and,thus, cold spots on the mixing vessel wall where condensation can occur.

A third approach we considered was to add electric heaters or electrictracing to the outside of the mixing vessel underneath the insulation.At temperatures above about 550° C., however, this approach leads tohigh cost with the technologies available. Furthermore, because heatloss is not uniform from the mixing vessel because of nozzles, vesselsupports and insulation imperfections, control of the electric heaterswould be complicated. The metal temperatures must be high enough at allpoints exposed to the potassium hydroxide vapor so as to avoidcondensation, but care must be taken to avoid overheating the mixingvessel walls, which can lead to unacceptably low metal strength. Also,as discussed above, the bolts on the nozzle flanges on very hotequipment preferably should not be as hot as the vessel contents toprevent leakage due to high temperature creep. This approach thereforewould result in either the nozzles being “cold” spots for condensationand corrosion or, alternatively, locations for increased risk ofleakage, depending on whether or not the electric heaters apply heat inthe area of the nozzle flanges.

A fourth approach we considered was to install an external jacket on themixing vessel such that a hot utility stream could be passed through thejacket to warm the vessel. However, such a jacket would need to bedesigned for the high temperatures and the pressure of the utilityfluid. It would be difficult or even impractical to adequately jacketnozzles including manways, even if this is considered to be desirablegiven the potential sealing problems at high bolt temperatures.Furthermore, for such systems as described above, the temperaturesrequired exceed the highest condensing temperature for steam and themaximum operating temperatures for commercially available organic heattransfer fluids. Thus, the heat transfer fluid in an external jacketsystem most likely would need to be a molten salt or liquid metal, whichare difficult to use, and this results in very high operating andcapital costs.

A fifth approach we considered was that the steam supply temperature tothe mixing vessel could be increased, which increases all of the mixingvessel temperatures and increases the difference between the mixturetemperature and the dew point of the potassium hydroxide. However, thereare metallurgical limits to how high the temperature can be. Fortemperatures up to 815° C. (1500° F.), various 300-series stainlesssteels can be used to construct pressure-containing vessels and pipes.At higher temperatures, however, more expensive metals must be used, andmaintenance costs increase. In general, though, increasing the operatingtemperature up close to the limit of metallurgy is a reasonable approachto reducing or minimizing the necessary flow rate of the dilution steam.

A sixth approach we considered was that the mixing vessel wall metalcould be upgraded to an alloy able to withstand, if possible, thecorrosion caused by condensing potassium hydroxide. Because of thehighly aggressive nature of potassium hydroxide at these hightemperatures, however, the metal costs can become prohibitivelyexpensive, which results in a large increase in capital cost for themixing vessel. Furthermore, if the potassium hydroxide is allowed tocondense, it will accumulate in the vessel, require periodic removal,and will not be fed to the reaction system as desired.

These and other deficiencies in or limitations of the prior art and thevaried considered adaptations of more conventional technologies to tryto address the condensation problem are overcome in whole or in part bythe improved methods for condensation reduction of this invention andthe related mixing vessel design

OBJECTS OF THE INVENTION

Accordingly, general objects of the present invention are to provideimproved methods for creating a hot vapor stream by mixing fluid streamsof different compositions so as to reduce or minimize vapor condensationand to provide a conceptual mixing vessel design suitable for practicingthe methods of this invention.

A principal object of this invention is to provide an economic way tokeep condensation from occurring on the walls of a mixing vessel, cooledby heat loss to the environment, where at least two streams, one stream(the dilution stream) being a hot vapor and at least one other stream(the injected stream) being either a pure-component liquid, liquidsolution, solid-liquid slurry, vapor, or gas with suspended solids, aremixed to produce an all-vapor mixture that typically would be coolerthan the dilution stream supply temperature. The potential condensablecomponents either are in the injected stream(s) or are created byreaction between components from multiple streams when mixed.

A specific object of this invention is to provide a conceptual mixingvessel design for mixing fluids at different temperatures to create avapor stream while reducing or minimizing condensation in the interiorof the mixing vessel by flowing the typically higher temperaturedilution stream through a baffle or shell region surrounding the centralcore of the mixing vessel and adjacent to the outer pressure wall of themixing vessel prior to mixing the fluids.

A more specific object of this invention is to provide a conceptualmixing vessel design, and methods for using same, to effect the mixingof a potassium hydroxide solution with a steam feed to acatalyst-containing dehydrogenation unit while reducing or minimizingcondensation of potassium hydroxide on the interior walls or otherexposed surfaces of the mixing vessel in order to reduce or minimizecorrosion.

Other objects and advantages of the present invention will in part beobvious and will in part appear hereinafter. The invention accordinglycomprises, but is not limited to, the methods and related apparatus,involving several steps and the various components, and the relation andorder of one or more such steps and components with respect to each ofthe others, as exemplified by the following description and accompanyingdrawing. Various modifications of and variations on the method andapparatus as herein described will be apparent to those skilled in theart, and all such modifications and variations are considered within thescope of the invention.

SUMMARY OF THE INVENTION

In general, this invention comprises a mixing vessel with an internalbaffle that is essentially in parallel with the pressure-containingvessel wall creating a generally annular buffer or baffle region. Thebaffle shields virtually the entire interior of the vessel pressure wallfrom the fluid mixture in the center of the vessel, while the hot vaporin the annular baffle region maintains the internal baffle at atemperature high enough to prevent, at least substantially, condensationon the mixing region side of the baffle.

One embodiment of this invention is shown in FIG. 1. A dilution streamis introduced at one end of the vessel to the annular space between thebaffle and the vessel wall. An injected stream enters a mixing region inthe vessel interior from the opposite end of the vessel, and theinjected stream is propelled towards the vessel outlet down theapproximate centerline of the vessel. The dilution stream flows thelength of the vessel in the annular space before mixing with theinjected stream. The baffle ends just before it reaches the entry pointof the injected stream, which may be at the end of a pipe extending intothe vessel. The dilution stream is introduced to the mixing region inthe vessel interior from the annular baffle region by flowing it aroundthe entry point of the injected stream The dilution stream surrounds theinjection stream at the entry point of the interior mix zone, andbuffers temperature variations in the vapor mixture at the entry pointat the interior baffle wall. The resulting vapor mixture flows thelength of the vessel in a counterflow direction relative to the flow ofthe dilution stream through the baffle region and exits at the same endwhere the dilution stream had entered the baffle region. As the combinedtwo streams flow through the core region of the mixing vessel, they mixand any changes in phase or reactions occur.

The present invention may be adapted to situations where there is morethan one injected stream.

In most cases, it is expected that the injected streams will have lessmass than the dilution stream, but this invention may be adapted to theopposite condition.

This invention applies to all operating pressures.

One embodiment of this invention involves a vessel where the baffle is arelatively thin internal vessel that can either welded to the pressurewall of the vessel or loosely connected.

Another embodiment of this invention involves a “jacketed” vessel wherethe annular baffle space is defined by two walls of similar thicknessand the annular space is sealed except for the inlet and exit.

This invention is particularly useful for reducing or substantiallyeliminating condensation in situations where the condensable compoundsare corrosive.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic cross sectional view of an embodiment of a mixingvessel according to the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of a mixing vessel in accordance with the presentinvention is illustrated schematically in FIG. 1. The methods of thisinvention will be better understood by reference to the followingdescription of FIG. 1, however, the invention should not be construed tobe limited to the description of FIG. 1 in any manner whatsoever.

FIG. 1 is a schematic cross-sectional view of a mixing vessel/vaporizer10 according to the present invention designed to reduce, minimize oreliminate, at least substantially, condensation in the interior of thevessel as well as around the fluid inlets and outlets. The condensation,which this invention is intended to reduce, minimize or eliminate, atleast substantially, alternatively may be by a compound or compounds inthe injected stream, or can be by one or more compounds that result fromthe chemical reactions of compounds in the various feeds to the mixingvessel. Mixing vessel 10, as shown in FIG. 1, comprises a generallycylindrical pressure- or vacuum-containing wall 12, preferablyfabricated of a metal, such as steel, which defines a hollow region offluid mixing zone 14 in the interior of the vessel. Wall 12 ispenetrated by a first fluid inlet 16 at a first (inlet) end of vessel 10and a fluid outlet 18 at a second (outlet) end of vessel 10. In apreferred embodiment, fluid inlet 16 comprises a nozzle 17 or otherfluid injection device, as are known to those skilled in the art, forinjecting a fluid 19, such as a potassium hydroxide solution, into themixing zone 14. In another preferred embodiment, fluid inlet 16 andfluid outlet 18 are approximately in axial alignment along thelongitudinal centerline 20 through vessel 10.

Wall 12 also is penetrated by a second fluid inlet 22 located inproximity to fluid outlet 18, i.e., at or generally near the second(outlet) end of vessel 10. As shown in FIG. 1, fluid inlets 16 and 22and fluid outlet 18 may comprise conduits extending through wall 12 orprojections from wall 12. Also as shown in FIG. 1, in a preferredembodiment, wall 12 may taper to a smaller diameter cylinder at theoutlet end. In another preferred embodiment of this invention, as shownin FIG. 1, wall 12 of vessel 10 is completely surrounded by a layer ofinsulating material 24, except possibly at the fluid inlets and outlet.

Mixing vessel 10 further comprises a baffle structure or inner wall 26,preferably fabricated of a metal such as steel, generally enclosingmixing zone 14 and spaced at least a small distance apart from theinterior side wall of 12 so as to create a generally annular-shapedregion or buffer zone 28 between the baffle 26 and the interior side ofwall 12. As shown in FIG. 1, the baffle 26 may be connected to andsupported in place by wall 12 at the outlet end of the vessel 10, outletnozzle 18, or by other support members. Baffle 26 terminates just shortof inlet 16. Second fluid inlet 22 is in fluid communication with bufferzone 28 such that hot vapor 30 can flow into buffer zone 28.

The operation of mixing vessel 10 in accordance with the presentinvention can now be understood. A hot vapor 30, such as steam, isflowed through fluid inlet 22 into buffer zone 28 near the outlet end ofvessel 10. Hot vapor 30 then flows through buffer zone 28 toward theinlet end of vessel 10 in a generally counterflow direction relative tothe flow of combined fluid through mixing zone 14. Baffle 26 is abarrier that effectively separates the contents of mixing zone 14 fromthe interior of wall 12 thereby protecting the interior of wall 12 fromany corrosive condensate. At the same time, the flow of hot vapor 30through buffer zone 28 maintains baffle 26 at a temperature high enoughto reduce or prevent condensation on the mixing zone side of baffle 26.

The following temperature conditions must be satisfied in accordancewith this invention: 1) the dew point of the dilution stream must bebelow the dew point of the combined mixture; 2) the equilibrium mixturetemperature (assuming homogeneous mixing of the fluid streams) must beabove the dew point of any compound that must be kept in the vapor phaseand 3) the temperature of the dilution stream in buffer zone 28 mustalso be above the dew-point temperature of the mixture. It is expectedthat in most cases the dilution stream will be both hotter and larger inflow relative to the injected stream or streams, but the presentinvention can be adapted to accommodate situations where the injectedstream(s) are hotter and/or larger in flow.

At the inlet end of vessel 10, baffle 26 terminates just before inlet16. In a preferred embodiment, an insulated sleeve 32 surrounds inletconduit 16 and terminates in a nozzle 17. As the flow of hot vapor 30passes through nozzle 17, the lower temperature fluid 19 is injectedinto the hot vapor 30 where it is entrained, mixed with vapor in mixingzone 14, and any phase changes from liquid and/or solid to vapor occurs.At the outlet end of vessel 10, mixed vapor 34 from mixing zone 14 flowsout of vessel 10 through outlet 18.

As shown in FIG. 1, the mixing vessel of this invention normally wouldbe cylindrical as is typical in industrial designs. Mixing vesselshaving other shapes and geometries, however, such as spherical orrectangular, also are within the scope of this invention. Also, inaccordance with this invention, the orientation of the mixing vessel maybe horizontal, vertical, diagonal or any other orientation.

In still another embodiment of this invention, the dilution stream maybe introduced to an annular space around a smaller-diameter outlet endof vessel 10 as shown in FIG. 1. This smaller-diameter annular spacehelps to distribute the hot dilution stream to the rest of the baffledspace.

The present invention addresses many, if not all, of the problems of theprior art fluid mixing techniques and has many advantages compared withthe prior art techniques.

1. Because the temperature of the baffle will, in most cases, be betweenthat of the dilution stream and the combined mixed stream, condensationon the baffle does not occur, or is substantially reduced, because thetemperature of the dilution stream is higher than the dew point of thecombined stream in the mixing region. The heat flowing to theenvironment through the vessel wall and insulation is supplied by theincoming dilution stream instead of being taken from the combined streamthat contains the compound or compounds that can condense and possiblycause corrosion.

2. If corrosion does occur, it will only affect the baffle, which can bereplaced at a lower cost than replacement of the entire vessel.

3. If the baffle corrodes, it does not result in a safety hazard,whereas corrosion on the vessel wall could result in hot and/orcorrosive vapors being released to the environment.

4. The temperature of the baffle wall generally will be fairly uniformbecause the baffle temperature mostly is determined by the temperaturesof the incoming dilution stream and of the mixture stream which are bothabove the dew points of compounds in the mixture stream, and is notaffected much by localized low temperatures of the mixing vessel wallcaused by insulation imperfections, nozzles, vessel supports and otherattachments. Therefore, cold spots that could result in condensationvirtually are eliminated. The temperature of the baffle can be increasedby narrowing the annular space to increase dilution stream velocities,which will improved heat transfer from the dilution stream to thebaffle, at a cost of higher dilution stream pressure drop.

5. Because of the complicated geometry of nozzles and vesselattachments, predicting localized metal temperatures has a high degreeof uncertainty n an unmodified, mixing vessel. By contrast, the bafflesystem of this invention reduces or minimizes the uncertainty about thetemperatures of the surfaces that are exposed to the combined stream.

6. One embodiment of this invention is to make the baffle out of ahighly corrosion-resistant metal, which is economically feasible becausethe baffle can be relatively thin compared to the mixing vessel wallbecause the baffle needs to be designed for only minimal differentialpressures. To provide the same protection for the vessel wall wouldrequire either that the entire vessel wall, which must be thick enoughfor the design pressure at the design temperature, be made of thecorrosion-resistant metal, or else the vessel must be clad with thecorrosion-resistant metal, which also is very expensive.

7. With the baffle system of this invention, manways and certain othernozzles can be internally insulated, which reduces heat loss, thusreducing operating costs, and also lowers the temperature of the nozzlebolts, which reduces the risk of leakage at the flanges. Without thebaffle, internal nozzle insulation is problematic because suchinsulation would be difficult to seal from the vessel fluids. If thereare condensable compounds in the vapor next to the interior of thenozzle, then these compounds will diffuse through or around theinsulation to the cold nozzle end where condensation, and possiblycorrosion, would occur.

8. In comparison with increasing the dilution stream flow, adding aninternal baffle reduces the size of the mixing vessel and reduces thecost of utilities.

9. In comparison with adding more insulation, the baffle approacheffectively eliminates the problem whereas adding insulation in mostcases only reduces it.

10. In comparison with adding electric heaters to the outside of thevessel, adding a baffle reduces cost, simplifies the installation andprovides a passive solution to the condensation problem withouthigh-temperature wiring and the need for multiple temperaturecontrollers that require maintenance.

11. In comparison with an external heating jacket, the baffle approachis far more economic at high temperature because an external heatingjacket requires an external heater and heat transfer fluids, whichdepending on the temperatures, may be exotic.

12. In comparison with upgrading the metallurgy to resist the corrosionresulting from condensation, the baffle can reduce the cost of materialsand avoid the accumulation of condensed material, which should be in themixed outlet stream, in the mixing vessel.

The following example will illustrate the practice of this invention Theexample, however, should not be construed to limit the appended claimsin any manner whatsoever.

EXAMPLE

Steam is to be mixed with a potassium hydroxide stream at a pressure of200 kilopascals absolute. The equilibrium mixture temperature is 700° C.after accounting for heat losses and the heat required to heat thepotassium hydroxide stream. If a mix vessel for this mixing step wasdesigned in accordance with conventional practice, rather than accordingto this invention, and assuming the coldest part of the vessel wall is600° C. because of heat loss and heat transfer limitations from themixture to wall, then the maximum amount of potassium hydroxide thatcould be injected would be 5.3 g-moles of KOH per 100 kg-moles of steamThis limitation is imposed by the vapor pressure of potassium hydroxideat 600° C.

By contrast, if this same fluid mixing step was carried out in a mixingvessel designed and operated in accordance with the present invention,then the metal exposed to the potassium hydroxide vapor could be nocolder than the outlet mixture stream temperature of 700° C., whichgives a much higher limit of 46.7 g-moles of KOH per 100 kg-moles ofsteam that can be added. Thus, based on a constant residence time forthe combined stream, the mixing vessel volume can be approximately ninetimes smaller by using a baffle system design in accordance with thisinvention.

It will be apparent to those skilled in the art that other changes andmodifications may be made in the above-described apparatus and methodsfor mixing fluids at different temperatures without departing from thescope of the invention herein, and it is intended that all mattercontained in the above-description shall be interpreted in anillustrative and not a limiting sense.

1. An apparatus for combining two or more streams that when mixedproduce a vapor stream containing one or more components that cancondense to form liquids and/or solids at temperatures above ambient,said apparatus comprising: a vessel having an outer wall; a baffle walllocated within said vessel and in proximity to said outer wall to createan annular space between said baffle wall and said outer wall forreceiving at least one dilution stream, a vessel interior space withinsaid baffle wall for containing a combined stream; at least one dilutionstream inlet extending through said outer wall for delivering saiddilution stream into said annular space; at least one dilution streamoutlet for delivering said dilution stream from said annular space tosaid vessel interior space; at least one injection fluid stream inletextending through said outer wall and said baffle wall for delivering aninjection stream to said vessel interior space and mixing said injectionfluid stream with said dilution stream to form a combined stream in saidvessel interior space; and at least one combined vapor stream outletextending through said outer wall for delivering said combined vaporstream from said vessel; wherein said dilution stream inlet delivers adilution stream comprising a vapor having a dew-point temperature thatis less than that of said combined vapor stream and delivers said vaporto said annular space at a temperature above the dew-point temperatureof said combined vapor stream.
 2. An apparatus as defined in claim 1wherein said vessel is cylindrical in shape.
 3. An apparatus as definedin claim 1 wherein said injection stream inlet is located at an oppositeend of said vessel relative to said mixed vapor stream outlet.
 4. Anapparatus as defined in claim 3 wherein said injection stream inletfurther is located along a vessel centerline.
 5. An apparatus as definedin claim 1 wherein said injection stream inlet includes a nozzle.
 6. Anapparatus as defined in claim 1 wherein said baffle wall opening fordelivering said dilution stream from said annular space to saidcombining space is located in proximity to said injection stream inlet.7. An apparatus as defined in claim 1 wherein said baffle wall isconnected to said vessel wall in proximity to said mixed vapor streamoutlet.
 8. An apparatus as defined in claim 1 wherein the exterior ofsaid vessel is provided with insulation.
 9. An apparatus as defined inclaim 5 wherein an interior injection stream inlet pipe leading to saidnozzle is insulated.
 10. An apparatus as defined in claim 3 wherein saidoutlet end of the vessel is tapered to a narrower diameter.
 11. Aprocess for combining two or more streams that when combined produce acombined vapor stream containing one or more components that cancondense to form liquids and/or solids at temperatures above ambient,said process comprising: (a) delivering at least one dilution stream ata first temperature into an annular space in a vessel between the vesselwall and a baffle and allowing said dilution stream to flow through saidannular space to a baffle wall opening and into an interior combiningspace, said dilution stream comprising a vapor having a dew pointtemperature that is less than the temperature of a final combined vaporstream wherein said first temperature is above the dew point of saidcombined vapor stream (b) delivering at least one injection stream at asecond temperature into said interior combining space; (c) combiningsaid dilution stream with said injection stream in said interiorcombining space to form said combined vapor stream at a final combinedstream temperature; and (d) withdrawing said combined vapor stream fromsaid interior combining space through a vessel outlet.
 12. A process asdefined in claim 11 wherein said dilution stream is delivered to one endof said vessel and flows through said annular space to said baffle wallopening and countercurrent to said combined vapor stream.
 13. A processas defined in claim 12 wherein said baffle wall opening is located inproximity to the point of delivery of said injected stream.
 14. Aprocess as defined in claim 11 wherein said dilution stream issuperheated steam and the injected stream is a liquid.
 15. A process asdefined in claim 14 wherein said injected stream is a liquid, aqueoussolution comprises an ionic alkali metal.
 16. A process as defined inclaim 15 wherein said ionic alkali metal comprises potassium.
 17. Aprocess as defined in claim 11 wherein said dilution stream contains acomponent that is reactive with a component contained in said injectedstream.
 18. A process as defined in claim 11 wherein said injectedstream comprises a pure-component liquid, liquid solution, solid-liquidslurry, vapor, or gas with suspended solids.
 19. An apparatus forcombining two or more streams that when mixed produce a liquid streamcontaining one or more components that will condense to form solids attemperatures above ambient, said apparatus comprising: a vessel havingan outer wall; a baffle wall located in within said vessel and proximityto said outer wall to create an annular space between said baffle walland said outer wall for receiving at least one dilution stream; a vesselinterior space within said baffle wall for containing a combined stream;at least one dilution stream inlet extending through said outer wall fordelivering said dilution stream into said annular space; at least onedilution stream outlet for delivering dilution stream from said annularspace to said vessel space; at least one injection fluid stream inletextending through said outer wall and said baffle wall for delivering aninjection stream to said vessel interior space and mixing said injectionfluid stream with said dilution stream in said vessel interior space;and at least one combined stream outlet extending through said outerwall for delivering said combined stream from said vessel; wherein saiddilution stream inlet delivers said dilution stream comprises a dilutionstream liquid having an initial solidification point temperature that isless than that of the combined stream and delivers said liquid to saidannular space at a temperature above the initial solidification pointtemperature of said combined stream.
 20. A process for combining two ormore streams that when combined produce a combined liquid streamcontaining one or more components that will condense to form solids attemperatures above ambient, said process comprising: (a) delivering atleast one dilution stream at a first temperature into an annular spacein a vessel between the vessel wall and a baffle and allowing saiddilution stream to flow through said annular space to a baffle wallopening and into an interior combining space, said dilution streamcomprising a liquid having an initial solidification point temperaturethat is less than the temperature of a final combined liquid streamwherein said first temperature is above the initial solidification pointtemperature of said combined liquid stream; (b) delivering at least oneinjection stream to said interior combining space; (c) combining saiddilution stream with said injection stream in said interior combiningspace to form said combined liquid stream; and (d) withdrawing saidcombined liquid stream from said interior combining space through avessel outlet.